1. Field of the Invention
The present invention relates to a sealed type battery provided with a safety valve means and a method of manufacturing the same.
2. Description of the Prior Art
A battery, for which a stabilized hermeticity is required for a long time, having a hermetic-sealing construction using an insulating member 53 formed of glass or ceramics, as shown in FIG. 1, has been known. In this case, a terminal pin 62 of one polarity passes through the insulating member 53 arranged in a through-hole of a metallic cover 52 in a fixed manner and an exterior can 51 serving as a terminal of the other polarity is fixedly mounted on the metallic cover 52 by the laser welding and the like.
This hermetic-sealing construction has a difficult point in that a cost is high. Accordingly, a battery having a construction, in which an insulating member 53 formed of resins is used, a metallic washer 63 being put on a lower portion of a terminal pin 62 of one polarity passing through this insulating member 53 to fix the insulating member 53, as shown in FIG. 2, and a metallic cover 52 being fixedly mounted on an exterior can 51 in the same manner as in FIG. 1, has been proposed (Japanese Utility Model Laid-Open No. 22753/1985).
Such a battery has a high hermeticity, however, when it is misused or used in an abnormal environment, whereby an internal pressure of the battery is increased, there is the possibility that the battery is broken. Accordingly, various kinds of safety valve means are provided.
In the battery having the construction as shown in FIG. 1, a part 51a of the exterior can 51 has a wall thickness less than the rest so that this part 51a may be broken, whereby preventing the battery from being broken, when the internal pressure of the battery is abnormally increased. But, it is difficult to control a thickness of the part 51a and to set an operating pressure, so that a sufficient safety can not be achieved.
In addition, with the battery as shown in FIG. 2, when a temperature of the battery is abnormally increased, whereby increasing the internal pressure of the battery, gases within the battery are received to the outside of the battery through an opened portion formed when the insulating member 53 made of resins is molten, a joint portion of the insulating member 53 with the metallic cover 52 or cracked portions of the insulating member 53 in order to intend to lower the internal pressure of the battery and prevent the battery from being broken. But, also in this case, it is difficult to set the operating pressure, so that the safety valve is inferior in accuracy.
On the other hand, a sealed type battery provided with a highly accurate safety valve as shown in FIG. 3 has been known (Japanese Utility Model Laid-Open No. 87458/1986). The battery shown in FIG. 3 is provided with a mouth-sealing plate 54 serving as a terminal of one polarity provided with a safety valve comprising a mouth-sealing cover 56 provided with a valve hole 55, a flat head plate 59 provided with a vent hole 57 and a cutting blade 58, a flexible thin plate 60 always closing the valve hole 55 and an elastic member 61. This mouth-sealing plate 54 is mounted on the opened portion of the exterior can 51 through the insulating member 53.
In the battery having the construction shown in FIG. 3, a highly accurate safety valve is obtained but since an opened edge of the exterior can 51 is cramped to an outside surface of the insulating member 53 after pouring an electrolyte at the assembly of the battery, a liquid 64 is accumulated on a joint portion of the insulating member 53 with the exterior can 51 or a joint portion of the insulating member 53 with the mouth-sealing cover 56, whereby the liquid 64 is apt to leak out. In addition, since a cramping diameter of the exterior can 51 by the opened edge is large, a difficult point is in hermeticity.